When plotting polar projections (-Jp) of the pole regions, grdimage connects the 0° and 360° longitudes correctly if the grid contains geographical data. grdview does not follow this behavior, there is a gap between x=0° and 360°. Enforcing periodicity with -nl+bpx or -nl+bg does not help.

The attached image shows the problem (plus some z-ordering issue). It was created with the attached grid and the following command:

I have added a new test script (that currently fails) to remind us to fix this. Actually, running your -JP in GMT6 trunk shows two other problems as well that I need to fix - all highlighted by grdview/wrap.sh test script.